Technical Field of the Invention
The present invention relates in general to optical systems, and in particular to optical systems including apertured micromirrors.
Description of Related Art
Conventional micromirrors can be found in the form of plain metallized mirrors, multi-layer dielectric mirrors or Photonic Crystal (PC) mirrors. For example, flat metallized micromirrors are typically used as wideband reflecting elements in micro-optical systems, such as an N×N optical MEMS switch, a Michelson interferometer, a monolithically integrated FTIR spectrometer or a Fabry-Perot interferometer. Cylindrical metallized micromirrors have also been introduced to form variable optical attenuators and to increase the coupling efficiency of MEMS tunable lasers. Recently, spherical metallized micromirrors have been utilized in micro-optical benches and optical cavities.
However, conventional metallized micromirrors are not capable of providing a transmission output from the mirror, and thus, cannot perform many desirable optical functions. Although thin metallized layers, on the order of a few nanometers, have been used to allow for transmission, controlling the thickness of the metal in a precise and repeatable way has proved difficult, thus rendering the process impractical, especially when the micromirror is integrated into an optical bench and the metal coating is applied on the vertical wall (sidewall) of the micromirror.
Dielectric and Photonic Crystal (PC) micromirrors, instead, can operate as partially reflecting/transmission elements in micro-optical systems, overcoming the limitations of the traditional metallized mirrors. For example, optical tunable filters have been developed from interleaved layers of silicon and air fabricated using deep etching technology on SOI wafers. However, the optical performance using such multi-layer mirrors is strongly dependent on the tolerance in the fabrication process due to the high sensitivity of the micromirror spectral characteristics to the layer thickness, verticality and smoothness. Therefore, the integration of such micromirrors with micro optical benches typically results in a reduced mirror reflectivity and limited bandwidth.
What is needed is a micromirror that can perform as a partially reflecting/transmitting optical element and that can be monolithically integrable into a micro-optical bench system.